Injection molding granular



July 15, 1947. K Re. 22,899

INJECTION MOLDING GRANULAR MATERIALS I 2 Sheets-Sheet Original FiledDec. 18, 1939 vEl 1 H! I I? m i low-uh:

n! wamau R. TucKeR aw/ Lam;

y 15, 1947. w. R. TUCKER INJECTION MOLDING AGVRANULAR "MATERIALSOriginal Filed Dec. 2 Sheets-Sheet 2 Imhntor wanna R. TuuuLR A item weReissued July 15, 1947 INJECTION MOLDING GRANULAR MATERIALS Warren R.Tucker, Dayton, Ohio, assignor to The Hydraulic Development Corp. Inc.,Wilmington, Del., a corporation of Delaware Original No. 2,359,013,dated September 26, 1944, Serial No. 388,477, April 14, 1941, which is adivision of Serial No. 309,797, December 18,

1939. Serial No. 588,442

9 Claims.

This invention relates to a method of injection molding in which thetemperature of the plastic material is more accurately controlled. Theinvention may be used in the injection molding of either thermosettingor thermoplastic resins, but is particularly adaptable to the molding ofthermosetting materials.

Heretofore, it has been more or less common to heat the material in theinjection cylinder by electric heating means, or the circulation of aheated fluid around the injection cylinder, whereby the granularnon-fluent material is gradually heated up to the injectable statebefore it reaches the injection nozzle and in this fluent state isinjected into the mold cavity. A popular practice has been to heat theinjection cylinder with induction heat and to control the temperature ofthe cylinder wall by a suitable thermostat. This method isdisadvantageous since it is impossible to impart an absolutely uniformtemperature to the cylinder wall as this temperature fluctuates as muchas 4 or 5. The result is that the temperature of the fluent materialinjected into the mold fluctuates several degrees. This isdisadvantageous since the temperature of fluency of the commonlyemployed plastic material is very critical.

My invention substantially eliminates fluctuation in the temperature ofthe injected material. This constancy of temperature is especiallyimportant in the case of thermosetting materials because, if they areheated above a certain critical temperature for any sustained length oftime, an irreversible reaction takes place, reducing their capability ofbeing rendered fluent and injectable. M invention overcomes thesedisadvantages of the prior art; practices by providing a uniformtemperature in the injection cylinder. While the invention relatesparticularly to the maintenance of a uniform temperature in theinjection cylinder of an injection molding machine, the principlesthereof may, if desired, be applied in the maintenance of a uniformtemperature in other portions of the injection molding machine, such asin a preheating chamber or in the mold halves.

The principal object of the invention is to hold the temperature in aportion of the injection molding machine at a uniform and constant levelat which the material will be injected or will be rendered or maintainedfluent.

Another object of the invention is to maintain the temperature of athermosetting resin uniformly at a point below the critical temperatureof the resin, and to inject the resin into a mold Application forreissue April 16, 1945,

2 in which it is raised to or above the critical setting point of theresin.

Still another object is to provide a progressively increasingtemperature in a portion of the injection molding machine whereby thetemperature in different stages is completely uniform and isprogressively increased as the plastic moves forward towards the mold.

Still other objects will more fully hereinafter appear.

This application is a division of my copending application, Serial No.309,797, filed December 18, 1939. s

In the accompanying drawings:

Figure 1 is a vertical sectional view of one form of an apparatusembodying the principles of the present invention.

Figure 2 is a similar view of another form of apparatus embodying theprinciples of the present invention and in which the temperature of theinjection cylinder is progressively increased to a point below thecritical setting point of the plastic, and is then injected into themold in which it is raised to a point above the critical setting point.

Figure 3 is a similar view of another form of apparatus embodyin theprinciples of the present invention and in which the fusion bath iselectrically heated by a spiral immersion heater disposed in the bath,the bath being composed of a material which is a non-conductor ofelectricity when solid and a conductor of electricity when molten,electrical contacts being disposed in the bath and operative to maintainthe bath at the melting point by maintaining a mixture of molten andsolid bath material in intimate contact with one another; the electricalcontrol mechanism is shown diagrammatically.

Figure 4 is a similar View but showing another method of maintaining thebath material at the temperature at which change of phase from the solidstate occurs; in this form of the invention the bath material is formedinto two zones, the minor zone being disposed around the rear portion ofthe injection cylinder and being maintained at a temperature slightlyabove the melting point or temperature of change of phase, and the mainbody of the bath material being maintained at the melting point and nearthe point wher it is all molten; the control portion of the bath at therear thermostatically controls the application of heat to the whole bodyof fusion material or the like.

Figure 5 is a transverse vertical section through an injection cylinderequipp d With a fusion bath.

and with still other means for maintaining the bath at the meltingpoint; in this view, the expansion of. the fusion materialupon attainingthe molten state is utilized to control the application of electricalenergy to the heating element in the bath; the heating element is shownformed and disposed in such manner as to promote circulation of the bathmaterial.

My invention involves the utilization of a bath of normally solidmaterial at a change of phase in a jacket surrounding the portion of theinjection machine to be heated as an accurate means for controlling thetemperature in that portion of the injection molding machine, As thefusionmaterial for the bath, I may use metals having a melting pointcorresponding substantially. to the temperature to be maintained in theportion of the machine in question. However, I may use other materialsthan metals which have a constant or fixed melting point and which areadapted to be held at the melting point for prolonged periods of timeand which may be melted and solidified indefinitely. As an example ofsuch other materials, I may use pure metals, chemical-compounds andeutectic mixtures, all of which melt and freeze at a constanttemperature. For example, I may use sulphur, naphthalene, benzophenone,and certain salts which have the desired melting point such as, forexample, potassium nitrate having a melting point of 337 C., a 45-55mixture of sodium nitrate and potassium nitrate, which has a meltingpoint of 218 C or a 55-45 mixture of sodium nitrate and sodium nitritewhich has a melting point of 221 C. As an example of still othermaterials which may be employed, I may. under certain circumstances makeuse of the transition or cryohydric points of crystalline hydrates,where this transformation temperature is sufiiciently high, this beinganother example of control materials having nonvariant points andcomprising a solid and a liquid, in admixture at the transitiontemperature. As examples of suitable alloys which may be employed',there may be mentioned an alloy consisting of equal weights of lead andtin, preferably with the addition of 0.1% of cadmium to improvevthefluidity of the alloy, relatively low melting points alloys of bismuth,tin, lead and cadmium, such as those enumerated under the headingFusible metals in the book, Campbells List of Alloys, 1930, page 52.Lead may be employed where a temperature of 327 is desired. An alloy of30% lead and 70% tin may be used where a temperature of 183 C. isemployed. In addition to the foregoing alloys, the fusible alloys setforth on page 555 of the Handbook of Chemistry, by Lange, 1934; or onpag 488 of Product Engineering," volume (Nov. 1939) may be used. It willbe understood that the fusible or like material is selected which has amelting or transformation temperature corresponding to that which it isdesiredto maintain in the injection molding machine heating chamber.

The fusible orlike material is placed in a jacket surrounding theheating chamber. This jacket is provided with heating means of the usualtype which has been heretofore employed directly around the heatingchamber. This heating means; may take the form of electrical resistanceelements, or heating passageways throughwhich a heated fluid such as hotoil is directed. Since the purpose of the present invention is to avoidthe fluctuation in temperature of a heated fluid, it is usuallypreferred to employ anelectric'heating. element at this point, theelectric heating.

element being controlled by a suitable rheostat or other controllingmeans. If desired, a pyrometer which is adapted to indicateand controlthe temperature of the fusible or like material may be used. There maybe provided thermostatic means operating in response to the temperatureof the bath material or to the temperature in the heating chamber,whereby the electric heating element is automatically energize orde-energized to maintain the proper temperature and to compensate forthe abstraction of heat from the heating chamber by the varied andnon-uniform amounts of plastic material passed through the heatingchamber.

By reason of the provision of a relatively large quantity of fusible orlike material which is maintained at its melting point and whichordinarily has a high latent heat of fusion, the passage of materialthrough the heating chamber does not ordinarily abstract suflicient heatfrom this body of fusible material to lower it below its melting point.In this way the temperature of the molten metal or the like does notdrop and, correspondingly, the temperature of the wall of the injectioncylinder and the temperature to which the plastic is heated, remainsconstant despite the abstraction of heat by the granular plastic. Thelarge volume of melted metal or the like at its melting point acts as alarge reserve of heat from which heat may be abstracted. intermittentlyWithout fluctuation in the actual temperature, advantage being taken ofthe phenomenon that the temperature of melting or of transition remainsconstant as long as the solid and the liquid phase are in intermixture.In this way, the present invention enables a reduction in fluctuation oftemperature in the heating chamber to a negligible If desired, 1- mayprovide suitable means for preventing the electric heating element fromheating the moltenmetal or the like above itsfusion or transition pointand for similarly preventing the moiten metal from dropping below itsmelting point, thus insuring that a mixture of solid and moltenmetal isat all times present. Preferably, this mixture should be insuch a statethat the application of only a small amount of heat will convert itentirely to a molten form,

thereby providing the maximum reserve of heat in the metal withoutallowing it to rise above the melting point. However, under certaincircumstances, the metal may be allowed to rise above'its melting pointslightly, since the specific heatof the metal will usually bevery'smallcompared to the latent heat of fusion and, therefore, thepassage of plastic through the heating chamber would soon lower thetemperature to the melting point without doing undue damage. The meansfor insuring that the metal or the like remains at the fusion ortransition point may take any suitable form. For example, it mightcomprise a small portion of the fusible metal separated from the mainbody of the metal and adapted to more readily respond to the abstractionof heat by the passage of plastic through-the heating chamber. Apyrometer or thermostat is. connected to this separate portion in suchmanner that either the operator may manually or the thermostat mayautomatically apply the electric current to the heating element tov anextent directly proporional to the drop initemperature of the separateportion of fusible metal, thereby preventing the temperature of the mainbody of fusible metal from dropping below the melting point. This meansmay take any other form of device for maintaining a fusible material atthe stage where it comprises both the solid and the fused material inintermixture and preferably at the point where almost all of the solidmaterial has been converted to the molten form.

When using molten materials in the manner heretofore described thedegree of temperature control over the plastic material passing throughthe heating chamber is very accurate, the injection temperature of theplastic being maintained constant at the melting point of the heatingmaterial. In the case of thermosetting resins the temperature of thematerial at the instant of injection is maintained below the criticaltemperature of the material and can be maintained sufficiently accuratethat the plastic material is injected while still in the granular state.The temperature of the material is then elevated while in the mold tobring the same to a fluent condition, at which time the chemical changeof the plastic occurs causing setting thereof.

The accompanying drawings portray several methods of carrying out theinvention. Referring first to Figure 1, reference numeral I designatesthe injection cylinder of an injection molding machine, in whichreciprocates the injection plunger 2. The injection cylinder is providedwith a screwed-in injection nozzle 3 and with a material spreader ortorpedo 4, and is adapted to inject granular or fluent material into themold cavity 5 formed by the cooperating mold halves 6 and I, mold half Ibeing stationary and mold half 6 bein clamped thereto by means of thehydraulic motor 8. Surrounding the injection cylinder l is a jacket 9 ofany suitable type adapted to retain the molten metal or the like andpreferably constructed with a highly heat conductive cylindrical wall inorder that the heat of the heating element may be readily transferred tothe metal II) or the like interposed between the jacket 9 and theexterior of the injection cylinder I. Surrounding the jacket 9 and inintimate contact therewith is an electrical heating element I I aroundwhich is disposed the heat insulating material I3. The electricalcurrent is supplied to the heating element II by the power lines I4 andI5, a rheostat I 6 being interposed, if desired, in the lead I5. Thetemperature to which the metal I0 is heated and the application ofelectric current to heating element Il may be indicated and controlledby the instrument I! having the heat sensitive element l8 disposed at asuitable point in the bath material. The instrument I1 is an ordinarycommercially available indicator and thermostatic control and is adaptedto maintain the temperature of the metal I I] at the temperature towhich instrument I! is adjusted.

In Figure 1, the mold halves G and I are cored and are adapted to have aheated liquid circulated therethrough by means of inlet pipe I9 andoutlet pipe 29. When operating with thermoplastic materials, the moldhalves B and 1 may be maintained at a temperature below the settingpoint of the plastic. When operating with thermosetting materials, theymay be maintained at a temperature above the critical temperature of theresin and will thus cause the resin to assume its infusible form afterthe expiration of the necessary interval.

In Figure 2 of the drawings, the general arrangement is similar to thatof Fig. 1 except that a series of separate zones for heating areemployed, a fusible or like material being used in each zone which has amelting or phase conversion point corresponding to a temperature desiredto be maintained in that zone. The zones Illa, "lb and lllc areseparated by partitions 2|. The individual heating elements Ila, llb andHe may be controlled manually, if desired, by the variable resistancel6a, I61) and IE0, electric current being supplied as before by lines I4and I5. It is preferable, however, to control the application of currentto the heating elements by means of the control instruments I'la, Nb andHe, as before. The materials Illa, I02) and IOc for the baths areselected with a view to having their melting or phase conversion pointscorrespond to the temperatures to be maintained in the zones of theinjection cylinder, or the temperatures maintained in the baths may beselected with a view to obtaining the desired heat transfer. Forexample, it may be desired to maintain around zone A a relatively lowtemperature in order to prevent softening of the plastic in this zone,a, somewhat higher temperature around zone B in order to begin thesoftening of the plastic, and a still higher temperature aroundthejorwardmost zone C so as to render the plastic completely fluent,this last temperature being, however, below the critical setting pointof the thermo-setting resin being injected. Or it might be desirable touse a high temperature around zone A in order to obtain very rapidtransfer of heat to the plastic material and to use a relatively lowtemperature around zones B and C in order to convert the material tofluent form but to prevent burning of the material, the temperature inthe final zone C being optionally just under the critical setting pointof the resin to maintain the resin fluent or to maintain the temperatureof the resin just below the point of fluency to permit the same to beinjected into the mold in a granular state. When injectingthermo-setting materials with the arrangement of Figure 2, the moldhalves 6 and I are heated to a temperature above the criticaltemperature of the resin by means of electric heating elements 22 or bythe circulation of a heated fluid as in Figure 1,

Instead of surrounding the fusion bath with the electric heating elementas shown in Figs. 1 and 2, a rod-like commercially available heatingelement may be spirally wound around the injection cylinder I within thematerial of the bath. An example of such a heater is the ordinarycommercially available Calrod immersion heater manufactured by theGeneral Electric Company. By using such an immersion heater,particularly in conjunction with the use of a metal as the bathmaterial, a perfect contact is obtained between the heater and the bath,whereby heat losses are minimized and rapid heating is assured.

It will be seen from the foregoing that the use ofa bath II] eliminatesthe necessity for a circulating pump for circulating the heated materialheretofore employed and prevents local overheating of portions of theinjection cylinder. In addition, it enables the maintenance of anexactly predetermined temperature of the bath and a correspondingtemperature of the plastic material. Where the materials employed forthe bath are good heat conductors, such as molten metal or fused salts,a better contact is obtained With the wall of the injection cylinder andwith the surface of the heating element, thereby resulting in faster andmore uniform heating of the plastic. Instead of using conducted heat forheating the bath, .1 may use induced heat, arranging the bath to act asthe low tension winding of a transformer and effecting heating in- "7ductivcly with eddy currents of high frequency. For the highertemperature'ranges, I may use molten metals or fused salts, whereas forthe lower temperature ranges, I may use the transformation temperaturesof crystalline hydrates, such as, for example, copper sulphate at 1100., barium chloride at 100 C., barium hydroxide at 78 0., sodiumsulphate at 32 0., manganese chloride at 58 C., trlsodium phosphate at.73 0., sodium bromide at '51 0., sodium carbonate at 35 C. and sodiumthiosulphate at 48 C. It will be understood that the plastic may notattain the temperature of the jacket, but may stay below the temperatureof the jacket, the temperature difference being determinedby theparticular plastic, the particular speed of operation, and theparticular die employed, the temperature of the jacket beingpredetermined by experiments conducted before the actual injectionprocess, and once having been determined, being maintained at thetemperature of change of phase as long as the particular conditions areutilized.

Instead of maintaining the temperature at the change of phase in thecase of fusible materials, I may, under certain circumstances carry itabove the fusing point and use an ordinary thermostatic control tomaintain it at approximately the desired temperature. For example, inthe case of an alloy melting at 90 C., I may operate with this alloymaintained at a temperature of substantially 100 C., or higher, ifdesired. In such a case, I prefer to use a highly heat conductivematerial for the bath, such as metal or fused salt in order to attainthe advantages of better heat conduction thereby as compared with thehot oil which has been heretofore commonly employed.

Referring now to the modification shown in Figure 3, the generalconstruction is the same as that heretofore described, except that aspiral rod-like heating element 23 is wound around the injectioncylinder I and is within the material of the bath, and this heatingelement is controlled by the state of the material of the bath. The bathmaterial 24 is carried within a suitable jacket 25 surrounded by heatinsulation 26. The material of the bath is such that it will not conductelectricity when solid but will conduct electricity upon the change ofphase, such as upon becoming molten. For example, the bath material maybe a fused salt such as the salts enumerated above, the salt beingselected which has the desired melting point and electrical conductingproperties when molten and when solid. Instead of using a fused bath, Imay, under certain circumstances, employ a crystalline hydrate at thetemperature at which-it loses water. In such case, the material belowthe transition temperature will not conduct electricity but above thetransition temperature will conduct electricity. In order to insure thatthe bath material 24 is maintained at the melting point or the like, Iprovide a pair of electrical contacts 21 which are adapted to beelectrically connected when the bath material therebetween becomesmolten and to thereby allow electrical current to flow through thesecondary of transformer 29 and through the winding .28 of solenoid 30,thereby opening switch 3| and opening the electrical circuit to heatingelement 23 which is normally established by reason of a spring normal-1y holding switch 3[ in closed Position, the incoming power lines beingdesignated as 32. The contacts 21 are Well removed from the heaterelement 23 so that a large portion of bath mathe melting point of thebath material.

terial 24 is in molten form before the circuit is established acrosscontacts 21. In this way, a large reserve of latent heat of fusion isavailable for heating the plastic in the injection cylinder. When switch3| is opened, the supply of electricity to heater element 23 is cut offand solidification of the bath material in the region of contacts 2'!may occur by reason of the loss of heat from the bath by radiation or byextraction thereof by the plastic material. By using the apparatus ofFig. 3, the necessity for using an expensive thermostat is eliminated,the bath itself being employed to control the application of electricalenergy and thereby to maintain the bath at the temperature of conversionand at a point where the major portion of the bath is in the convertedstate.

In Figure 4 there is shown an apparatus where in the same generalarrangement is employed as in Figure 3, except that the necessity foremploying a material which is an electrical conductor when converted buta non-conductor when in the solid state, is eliminated, and wherein adifferent method of maintaining the bath at the temperature ofconversion is employed. In this embodiment, a molten metal bath may beemployed as well as any of the materials which would besuitable for usein the apparatus of Figure 3. The bath is divided into two portions, amain portion 3:3 and a relatively small control portion 34 which isdisposed around a rear portion of injection cylinder I, these portions33 and 34 being separated-by a. partition 35. A heater element 23 isemployed as in Fig. 3, with the major portion thereof disposed in themain portion. 33 of the bath and with a proportionately larger por tionin the control section'34. For example, there is illustrated the use ofone and one-half turns of the-spiral heating element in control section34, whereas-the spacing of the turns in the main portion 33 is suchthat-only one turn is used in a portionof bath 33ccrresponding in lengthand size to control'bath 34. A thermostat 35 is provided having asensitive element 3'! disposed in the control bath 34 at a considerabledistance from the heating element 23, and this thermostat 35 is adaptedto actuate a snap switch 38 disposed in one of the incoming power lines32 and to thereby cut off the application of heat to heater 23 when apredetermined temperature in the control bath 34 has been reached.Thermostat 35 need not be-extremely sensitive and, therefore, needgnotbe unduly expensive, it being satisfactory if thermostat 36 isresponsive to temperature changes of the-order of 3 or 4F. Thermostat 36is adjusted so as to maintain the temperature in control portion 34- at3 or 4 above For example, if thermostat 36 is accurate to within 3plusonminusgit may be set to operate at a temperature of say 4 above themelting point of the bath material. Due to the fact that thermostat 36issetttooperate at a temperature slightly above the melting point andtothe fact that the proportionate heat applied to the control porion 34 isgreater than that to the main portion 33, the

result will bethat the main bath. 33 will be maintainedat the meltingtemperature and at a'point where ,it is practically all in the molten orconverted form. The maintenance of control bath 34 at a highertemperatureis not harmful because the plastic at .the rear of theinjection cylinder is granular and is not capable of being injured bythe excessive temperatureat this point, although the subjection of thefluent plastic to such a temperature might convert it to the infusibleform. From the foregoing, it will be seen that the arrangement of Fig. 4provides a simple and inexpensive means of maintaining the main body ofthe bath at the conversion temperature. Referring to the modificationshown in Fig. 5, the bath comprises material which expands upon becomingmolten, such as suitable known metals having this characteristic, andthis expansion isemployed to break the circuit to the electric heatingelement when the entire body of metal or the like has become molten. Thebath material as is heated by electrical heating element ll which isgenerally of the type described in. co-pending application of I. B.Lawyer, Serial No. 231,637, filed September 26, 1938, and is adapted tocause convection circulation of the material of the bath and to therebyeliminate local overheating. As the material of thebath becomes molten,it urges outwardly a plunger 42 which is normally spring pressedinwardly and which operates within a cylinder 43 mounted in the wall ofthe jacket. When plunger 42 moves outwardly due to the expansion of themetal or the like, it opens a snap switch 44 disposed in one of thepower lines 32 leading to the heater 4|, cutting off the supply ofelectrical current and allowing the bath 4!! to remain at its molten.temperature and preventing it from being heated above the temperature ofmelting. As heat is abstracted from bath 4!], the bath shrinks andplunger 42 is spring-pressed inwardly, causing snap switch 44 to close,thus again energizing heater 4! and causing the temperature of the bath40 to rise. By disposing the plunger 42 at the top of the bath and at apoint well removed from heater element 4i, it is insured that a largeportion of the bath 4B is in molten form before the electric current iscut ofi to heater 4|. Thus, by taking advantage of the property of thebath material of expanding upon change of state to the molten form, I amenabled to maintain the temperature of the bath at the melting point andnear that point where it is all molten but without raising itstemperature above the melting point, without the use of an expensivethermostat.

In Figures 3 and 4, an expansion space 39 is provided above the bath toallow for expansion thereof upon heating, and in the disclosure of Fig.3 the expansion of the heating material can make or break electriccircuit through the contacts 21, upon a rise or fall of the level of thematerial.

From the foregoing description, it will be seen that I have devised aninexpensive and effective method and apparatus for heating a plasti to aconstant temperature using the latent heat of a heating material, thismethod and apparatus being particularly applicable to the injectionmolding of thermo-setting materials which are exceedingly susceptible tosmall increases in temperature over a critical temperature, although theinvention may equally be applied to thermoplastic materials Whereconstant conditions of operation are desired. These results areaccomplished in a preferred form by the maintenance of a bath in directheat conducting relationship with the injection cylinder, this bathbeing maintained at the constant temperature at which it undergoes achange of phase from the solid state. I consider that invention residesnot only in the method and apparatus for injection molding, but also inthe particular controlling means of Fig. 3, for example. It will be seenthat I have devised mechanism which not only maintains the bath materialat the temperature of change of phase, but which maintains it at a pointwhere the change of phase is almost entirely complete, so that the largereserve of latent heat attendant upon extensive change of phase isavailable at a constant temperature to heat the plastic.

The process may be carried out by heating the granular or powderedthermo-setting plastic in the injection cylinder to a suitable lowtemperature at which it retains its granular form, and injecting itunder pressure into the mold while it retains its granular form, thetemperature to which the mold is heated and the pressure to which thegranular material is subjected by the injection plunger after it is inthe mold, being sufiiciently high to cause the material to flow into ahomogeneous form and to subsequently set. In the case of granularthermoplastic materials the mold is heated sufficiently and theinjection pressure exerted on the granular plastic in the mold is suchas to cause the granular material in the mold to fiow to take the shapeof the article after which the mold cools or is cooled to harden thearticle.

The granular thermo-setting plastic may be preheated in the injectioncylinder to a temperature at which it is sufliciently soft'to beinjected (say to C.) under the usual injection pressures and theninjected into the mold while it retains its unreacted state, the moldbeing heated as before to a temperature above the critical temperatureof the resin and supplied with sufficient heat at the temperature to setthe article.

I wish it to be understood that I intend to include as within myinvention such modifications and adaptations'thereof a may be necessaryto make it suitable for varying conditions and uses and as fall withinthe scope of the appended claims.

Having thus full described my invention, what I claim as new and desireto secure by Letters Patent is:

l. The process of injection molding which comprises heating granularplastic in an injection chamber to a relatively low temperature to heatthe same but to retain its granular form, and injecting it in granularform into a hot mold to prevent any substantial reduction in temperaturein the transfer from the injection chamber to the mold, the mold beingheated'sufliciently and the injection pressure applied on the materialin the mold being suflicient to cause the granular injectecl material torapidly plasticize and flow into a homogeneous article taking the formof the mold.

2. The process of injection molding which comprises heating granularunreacted thermosetting plastic in an injection chamber to a relativelylow temperature to retain its granular unreacted form, injecting it ingranular form into a hot mold, the mold being heated sufficiently andthe injection pressure applied on the material in the mold beingsufficient to cause the granular injected material to plasticize andflow into a homogeneous article taking the form of the mold, and toelevate the temperature of the granular material within the mold toreaction temperature for permanently setting the same.

3. The process of injection molding Which comprises heating a granularplastic in an injection chamber to a controlled low temperature at whichit retains its granular form, of injecting the heated material while ingranular form and at the low temperature into a hot mold that is at atemperature substantially above the temperature zasee of the plasticmaterial torapidly elevate the temperature of the plastic to that of themold whereby to plasticize the same, and of causing the plasticizedmaterial to set;

4' -T-he"process of injection molding which com= prises elevating thetemperature of a granular plastic in an injection chamber to arelativelylow temperature at which it retains its granular form by subjecting theplastic to the action-of latent heat de'riveddirectly from a bodyoficnormally solid material maintained at a temperature at which thematerial undergoes a change of'phase from the solid state, and injectingthe plastic'material in granular form into' a .mold heated to atemperature substantially above the temperature of the granular plastic,themold be'ing'heated sufficiently and the injection pressure ap'pliedon the material in the mold being suflicient to cause the granularinjected material to plasticlze and flow into a homogeneous article thes'olid'state, and. injecting the'plastic in g'ranular form into a moldheated to a'temperature substantiallyabove the temperature of thegranul'a'r plastic; the :mold being heated sufiiciently and'theinjection pressure applied on the material'in the mold being'suflicient'to .cause the granular-injected material to plasticizeand'flow. into a homogeneous article taking the form of the mold and tosubsequently react. and set to the solid'state; 1 6. The process ofinjection molding which comprises elevating the temperatureera-"granular plasticin a'plurality of independentstages to amaximumt'emperature= {at i which it retains its granularforrm'individually controlling the temperature 50f each of the stages, and :ofinjecting thepla'stic into amold in granular form at the temperature ofthefinal stage. 1

l'Il'ie-process of injection molding which comprisestsequentlallysubjecting granular plastic :to

the action of latent heat derived directly from a plurality of normallysolid bodies of material maintained at different temperatures and atwhich the several independent bodies undergo a change in phase from thesolid state to elevate the temperature of the granular plastic in aplurality of stages to a maximum temperature at which it retains itsgranular form, individually controlling the temperature of each of thestages, and of injecting the plastic into a mold in granular form and atthe temperature of the final stage.

8. The process of injection molding which com prises heating a zonethrough which plastic material passes to a'temperature substantiallyequal to the physical transformation temperature of a heating materialwhen passing from the solid to the liquid state and surrounding thezone, of passing granular plastic material through the zone to elevatethe temperature thereof to that of the zone without changing thegranular condition of the material, of ejecting the plastic ftomthe zoneinto a mold in a granular state, and of controlling the temperature ofthe heating material to maintain the same at said transition temperaturethereof to maintain the temperature of the granular plastic constantjust prior to ejection.

9. The process of injection molding which com prises initially heatinggranular plastic to a relatively low temperature to heat the same but toretain its granular form, and injecting it-in gran- REFERENCES CITED Thefollowing references are of record in the file of this patent:

I V UNITED STATES PA'IIEINTS Number .Date

Name ,7 2,235,324 Moreland Mar. 18, 1941 1,402,705 Apple Jan. 3, 1922

